The World Health Organization annually reports several million cases of food poisoning caused by Salmonella spp. In 2009 the European Food Safety Authority reported over 100,000 cases, indicating that the problems with Salmonella spp. are not confined to developing countries and threshold countries alone.
Salmonella spp. are zoonotic germs, meaning they are transferred from animals or animal products to humans. The most common sources of Salmonella spp. in our diet are fresh poultry meat, fresh pig meat, eggs as well as fresh milk. Between 3% and 5% of the registered cases of human salmonellosis have been associated with exposure to exotic pets such as turtles, snakes, iguanas and lizards (Rabsch et al. 2003, CDC. Salmonella surveillance: annual summary).
This threat to consumer health lead the EC legislative authorities to release the EC regulation number 2160/2003 on the control of Salmonella and other specified food-borne zoonotic agents. This regulation sets a threshold level “absence in 25 grams” for fresh poultry meat for the currently most pre-dominant human pathogenic Salmonella species Salmonella enterica spp. enterica serovar enteritidis (short Salmonella enteritidis or S. enteritidis; further in the text the short designations are used) and Salmonella typhimurium. 
The pressure to reduce the prevalence of these harmful pathogens is shared by all parties involved in food production. However, the currently used strategies to avoid, reduce and treat Salmonella spp. in the primary meat production, in slaughterhouses and in meat processing facilities are not efficient. Even strict adherence to state of the art hygiene regulations cannot prevent Salmonella outbreaks as the case numbers reported above demonstrate.
A commonly used method to avoid Salmonella spp. infection in livestock and poultry was the use of antibiotic growth promoters. At least 8 antibiotic growth promoters could be found among the “approved animal drug products” on the web site of the US FDA, with indications for use to increase weight gain or prevent infection. However, since the 1960s scientific evidence pointed out that the development of bacterial resistance to antibiotics is linked to the use of antibiotics in animal feed. In the course of the fight against bacterial antibiotic resistance the WHO issued a number of recommendations to its member-states, which included:                the termination of the use of any antimicrobial growth promoter if the same or a related product is also used in human medicine;        the replacement of antimicrobial growth promoters with non-antibiotic alternatives;        only authorised use of antimicrobial growth promoters;        monitoring of the amounts of antimicrobial growth promoters used for risk assessment purposes.        
Current EU law bans the preventive use of antibiotics in farm animals. The therapeutic use of antibiotics, while still legal and applied liberally, does not result in salmonella-free animals either, due to the increased number of Salmonella ssp. isolates which are resistant against the antibiotics in use.
In the 1990s a vaccination approach to prevent bacterial infections in domestic animals has been developed. Currently, a number of commercially available vaccines (both live attenuated and inactivated) are in use to protect pigs, horses, cattle, chicken and turkey against Salmonella Newport, Salmonella gallinarum, Salmonella enteritidis, Salmonella choleraesuis and Salmonella typhimurium. Five clinical trials and 23 challenge studies have been done to evaluate the efficacy of vaccination to reduce Salmonella prevalence in live and slaughtered swine (Denagamage et al. 2007. Foodborne Pathog. Dis. 4:539-49) and the available evidence suggests that vaccination is associated with reduced Salmonella prevalence in swine at or near harvest. In poultry vaccination against Salmonella of laying hens, broilers and breeders was found effective and decreases the level on farm contamination as well (Berghaus et al. 2011, J. Food Prot. 74:727-34.) However, vaccination also has some drawbacks, especially when considering short lived animals like broilers. First, the immune system of chicks is developing slowly. The protection granted by a vaccination does not cover a period of several days after hatching, in which the chicks unfortunately are very susceptible to infections by Salmonella spp. Second, most vaccines provide protection against a single Salmonella species, cross protection against several isolates is rare. Thus, there is an inherent risk that a secondary Salmonella infection might break out despite vaccination against a first. Accordingly, there is still a high demand for alternative methods to fight Salmonella spp to replace the use of antibiotic growth promoters and complement the vaccination approach.
The idea to use bacteriophages to fight pathogenic bacteria is known for a long time. Indeed, already the co-discoverer of bacteriophages, Félix d'Hérelle, used bacteriophages to treat various bacterial infections almost a century ago. Since then numerous studies, experiments and therapeutic treatments, many of which were performed in the countries of the former Eastern Bloc, provided ample evidence for the safety, efficiency and efficacy of bacteriophage therapies. However, only recent advances in the areas of genome sequence analysis and bioinformatics as well as improved protocols to purify large quantities of bacteriophages, see for example EP2195418 or Smrekar et al. 2011 (Smrekar et al. 2011. J. Sep. Sci. 34:2152-58), made it possible for bacteriophages to also realize their potential in the Western World (Monk et al. 2010. Lett. Appl. Microbiol. 51:363-9).
It is the scope of this invention to provide natural, safe and efficient methods to fight Salmonella spp. in the entire value chain from farm to fork. The proposed methods are based on the use of specific bacteriophages to specifically and efficiently fight their natural host bacteria. Furthermore, the aim of the present invention is to provide new bacteriophages useful against microorganisms, in particular, Salmonella spp.